It is well known to mix elements having high tensile strength in composite subsequently hardening soft material such as concrete and ceramics which only offer a small resistance to a tensile force. These elements are typically short pieces of wire, made of steel, glass fibre or other materials which, when mixed up in the material with a lower modulus of elasticity, results in a two-phase material of improved strength.
Elements of various forms have been disclosed in a number of prior patent documents, the below listed documents having been considered in the preparation of this specification:
U.S. Pat. No. 3,429,094 to J.P. Romualdi
Canadian Patent No. 1,038,642 to Ostling, et al.
Canadian Patent No. 1,037,733 to Moens, et al.
Canadian Patent No. 875,073 to Claire G. Ball, et al.
U.S. Pat. No. 1,976,832 to C.S.Brown
U.S. Pat. No. 3,900,667 to Moens
U.S. Pat. No. 3,953,953 to Marsden
U.S. Pat. No. 4,233,364 to van Thiel
Canadian Patent No. 1,020,331 to Lankard, David R.
Canadian Patent No. 1,092,388 to Curnow, et al.
A number of these documents, such as, U.S. Pat. No. 3,429,094 to Romualdi, and Canadian Patent No. 1,038,642 to Ostling et al, disclose the use of straight wire elements or fibres, the Ostling patent disclosing the use of elements of substantially rectangular cross-section and small thickness in relation to their length and width formed of steel flakes, with the shape tapering towards the ends of the flakes. The flakes have a thickness of about 0.1 mm to about 0.5 mm and a length of at least about 100 times the thickness.
As illustrated by the Ostling patent, it is recognized that the length to width ratio, or aspect ratio of an element is an important factor in the effectiveness of the element in enhancing the material properties of the final material. Generally, elements having a high aspect ratio provide more desirable characteristics, however such elements are more liable to "clumping" or "bailing" producing problems in handling. In Canadian Patent No. 1,037,733, to Moens et al the preferred ferrous reinforcing elements have a thickness of between about 0.1 mm and 1 mm and length to thickness ratio between about 50 and 200.
It is also recognized that the properties of the material are related to the total surface area of the reinforcing elements, Canadian Patent No. 875,073 to Ball et al disclosing the use of known round or flat reinforcing filaments and the improvements available when compared to round filaments of comparable weights.
It is further recognized that the anchoring of elements is improved by providing elements which are not straight or have an irregular shape. U.S. Pat. No. 1,976,832 to Brown discloses reinforced inserts in the general form of a dumbbell. U.S. Pat. No. 3,900,667 to Moens discloses a wire element consisting of a substantially straight wire having at both extremities a bending in the form for which the hooking in of two neighbouring elements is not possible. This is disclosed as a means for overcoming the problems associated with prior art elements formed in a shallow U-shape.
U.S. Pat. No. 3,953,953 to Marsden discloses elements having enlarged ends. These are formed by folding the edges of a strip of sheet metal onto itself or by edge rolling a strip. In both cases, the reinforcing element is formed by shearing the strip after its edge has been modified. A somewhat more complex fibre shape is disclosed in U.S. Pat. No. 4,233,364 to van Thiel, which discloses anchoring fibres having flattened and enlarged ends, with projections extending from the ends and protuberances provided along the body of the element.
Canadian Patent No. 1,020,331 to Lankard discloses a method of forming large thin shell structure members such as ferro-cement boats using a wire mesh reinforcement and Canadian Patent No. 1,092,388 to Curnow et al discloses the uses of multifilament strands of carbon fibres for reinforcing cement.